Submarine repeater pentode P.O. type 10P, 1950-1970

Submarine repeater pentode P.O. type 10P, made by the Post Office, England, 1950-1970.

Valves used in submarine telephone cables need to be very long lasting, due to the effort and cost involved in retrieving a cable from the seabed in order to replace one. Unlike some of the previous valves made by the Post Office, the 10P valve was designed specifically for use in submarine repeaters, rather than being a modification of existing valves. They were trialled in a cable laid across the North Sea, the Anglo-Swedish cable, in 1960, but found their main use in the CANTAT-1 telephone cable that connected the UK and Canada from 1961.